Gouache. 16.5cm by 21.5cm. Signed l.r.: Johann G Hackert, f. 1769.
The German-born artist, who died at the age of only twenty nine, was the younger brother of the more famous Jacob Philipp Hackert (1737-1807) who spent most of his working life in Italy and was regarded as the finest German landscape painter of the late 18th Century.
Today, Castel Gandolfo is part of the Vatican Estates and is the papal summer palace.